Plate boundaries Flashcards
What are some characteristics of divergent boundaries?
Plates move apart
Spreading centre - sea-floor spreading
Iceland is an example
New oceanic crust created from the extrusion of basaltic magma
The oceanic crust gets older and denser further from the boundary (ridge push)
Shield volcanoes
Earthquakes are virtually non-existent
Partial melting of the upper lithosphere
Fissure eruptions
Rift valleys may form
What is Continental Drift and who proposed the theory?
Alfred Wegener proposed the theory of Continental Drift which was the idea that the continents were moving around gradually over geological time
What are some aspects of rift valleys?
Crust fractures (normal faults)
New rocks form new oceanic crust
New sea made
Magma is produced by partial melting
Volcanoes and igneous rocks form in the valley
Convection currents stretch the Lithosphere
New crust forms
An example is the East African Rift Valley
What are some characteristics of convergent boundaries?
Plates move towards each other
One plate subducted under another: oceanic under continental, continental under continental or oceanic under oceanic
The denser crust is subducted (oceanic)
Violent volcanic eruptions likely occur due to hydration melting (volatile magma)
Violent earthquakes will occur along the Benioff Zone
Formation of volcanic island arcs, ocean trenches and volcanoes
Magma forms by partial melting
Upward movement of the mantle through decompression melting
An example is The Pacific Ring of Fire
What are some characteristics of conservative boundaries/transform faults?
Any two plates slide past each other
Sometimes, they get stuck, causing stress and strain to build up until the plates slip past each other in an earthquake
Fault line
There are no volcanoes, as there are no places for the magma to erupt out of
Crust is conserved
An example is the San Andreas fault
What are some characteristics of collision zones at convergent boundaries?
Two continental plates collide
Similar densities, so no subduction
No volcanoes
Plates buckle and crumple against each other
Tectonic uplift, which leads to orogeny
Formation of young fold mountains
The Himalayas are an example
The heat produced in collision causes partial melting
Magma rises and intrudes the crust and cools to form granite batholiths
The oceanic crust between continents is subducted and destroyed
What is some of the evidence for continental drift?
Jigsaw fits of the coastlines of continents, e.g., South America and Africa
Fossils found on multiple continents of trilobites and other extinct organisms like the mesosaurus
Glacial deposits are found in warm regions and coal deposits found in cold regions
Matching mountain chains and geology - similar rock sequences
Magnetism (remanent)
How was it later found that the continents were moving?
By the movement of tectonic plates
